1. Field of the Invention
The present invention relates to a recording water-based ink to be used in printers, recording equipment or writing utensils for industrial, office or home use, as well as to a recording method using the ink. More particularly, the present invention relates to an ink and a recording method with the ink suitable for a recording medium having a water-based ink receiving layer provided on a substrate (base paper) suitable for ink jet recording. More specifically, it relates to a water-based ink having sufficient properties as an ink and properties contributing to improvement of the recorded image and a recording method utilizing the same.
2. Related Background Art
In the recording media for ink (hereinafter simply called recording media) having satisfactory ink absorbing properties and capable of providing a high quality image, there is recently a commercialized recording medium employing an alumina hydrate as an inorganic pigment for the ink-receiving layer. Such a recording medium having the ink-receiving layer of alumina hydrate shows satisfactory fixation of the dye contained in the ink as a colorant because of the positive charge of alumina hydrate. In addition, because of the high transparency of alumina hydrate, it has characteristics superior to the conventional recording media in providing an image of high print density and good color development, and of high surface gloss, allowing formation of photographic images. hydrate as an inorganic pigment for the ink-receiving layer. Such a recording medium having the ink-receiving layer of alumina hydrate shows satisfactory fixation of the dye contained in the ink as a colorant because of the positive charge of alumina hydrate. In addition, because of high transparency of alumina hydrate, it has characteristics superior to the conventional recording media in providing an image of high print density and good color development, high surface gloss allowing formation of photographic images.
Recently, digital cameras have become very popular, and the recording medium for printing image information of digital cameras is required to have not only a high image quality but also photographic gloss in order to form images similar to a silver halide photograph. When the ink-receiving layer utilizing alumina hydrate is formed on a film by applying a coating liquid containing alumina hydrate, an image with photograph-like gloss is obtained, but when the substrate is a fibrous substrate such as paper, photograph-like gloss cannot be obtained by merely using an alumina hydrate coating liquid for the ink-receiving layer. In such a case, therefore, a process such as a supercalendering process or a casting process is used for providing a glossy ink-receiving layer. The casting process, especially, can provide an image having gloss similar to the silver halide photograph.
The aforementioned ink-receiving layer containing alumina hydrate shows an excellent colorant-fixing ability because alumina functions as a cationic reactant to an anionic dye. In order to obtain a recording medium of photographic gloss, it is already known to form an ink-receiving layer with alumina hydrate and polyvinyl alcohol (a binder) by the casting process. For a glossy ink jet recording medium, especially, there is proposed an improvement in the cast coating method including re-swelling of the receiving layer (for example, see Japanese Unexamined Patent Publication No. 2001-138628).
Now, the image quality obtained by an ink jet recording on such a recording medium has become very fine, comparable to that of a silver halide photograph, which is regarded as a representative of high image quality. Thus the ink used for such a high quality image recording requires more strict quality control.
One problem is the presence of impurities in the ink derived from impurities remaining in raw materials of the ink such as a colorant, or derived from the impurities in the constituent materials of the recording apparatus, especially the ink container, such as polypropylene (PP) or polyethylene terephthalate (PET). Such impurities contaminating the ink cause clogging in the recording ink feed path or deterioration in the feed characteristics, and are problematic, particularly in high image quality recording.
Impurities in the ink, either resulting from contaminants of a colorant not removed during the preparation process, or eluted from the ink tank or ink supply system, have been recognized as a problem. In many cases, such impurities cannot be removed, or even if they could be removed, further purification costs would become an obstacle in view of supplying an inexpensive product to the users.
In consideration of such situation, there is proposed a method of maintaining the total content of calcium, magnesium, manganese, iron, aluminum and silicon contained in the ink at 20 ppm or less thereby improving the nozzle clogging or resolving a kogation problem in a thermal ink jet recording utilizing heat as an ink discharge energy (cf. Japanese Patent Publication No. 3-48953).
Also a technology for enabling stable image formation against ink contamination with impurities eluting from the constituent materials of the recording unit such as the ink tank is disclosed, defining the relationship between the amount of silicon eluted from the ink absorbent member of the ink tank and the stable ink jet recording properties (cf. Japanese Unexamined Patent Publication No. 11-198399).
As explained above, the problem of impurities contaminating the ink, for example, those derived from the colorant impurities or those eluting from the constituent materials of the ink tank or the ink supply system, and countermeasures therefor have been studied, but not with satisfactory results. Presumably, it is because these countermeasures are limited to confining the impurity content to a certain level or less in the ink.
The above problem is especially conspicuous with an ink jet recording apparatus which ejects small ink droplets whose amount is 5 picoliter or less.